1. Field of the Invention
The present invention relates to a photochromic curable composition suited for the production of a photochromic cured product having excellent optical properties such as a high refractive index and a large Abbe's number, having favorable photochromic properties such as a large color density, and having good fatigue resistance, and to a photochromic lens obtained by curing the photochromic curable composition.
2. Prior Art
Photochromism is a phenomenon which is drawing attention in these several years, and stands for a reversible action of a compound; i.e., a compound quickly changes its color when it is irradiated with light containing ultraviolet rays such as of sunlight or light of a mercury lamp, and resumes its initial color when it is no longer irradiated with light and is placed in a dark place. The compound having such a property is called photochromic compound. The compounds having a variety of structures have heretofore been synthesized and proposed.
A photochromic plastic lens is the one that utilizes the photochromism. For example, Japanese Unexamined Patent Publication (Kokai) No. 124790/1991 proposes a photochromic curable composition obtained by dissolving a photochromic compound in a radically polymerizable monomer, and discloses a method of obtaining a photochromic resin by curing the photochromic curable composition. Particularly, this publication teaches the use of the cured product as a photochromic lens. However, many of the cured products taught in these publications have refractive indexes which are not less than 1.55.
It has been desired to provide lenses for spectacles having ever small thicknesses. Therefore, improvement has been forwarded extensively in order to provide a resin that exhibits a high refractive index, and a variety of cured products and monomer compositions have been studied and proposed for producing lenses. However, few studies are concerned to the photochromic lenses having refractive indexes in excess of 1.56, and no technology has been positively developed except the one disclosed in Japanese Unexamined Patent Publication (Kokai) No. 169918/1996. Many styryl compounds have been studied as general highly refractive polymerizable monomers. However, these highly refractive cured products have poor fatigue resistances in the photochromic properties compared to that of the lowly refractive cured products and, besides, have small color densities and are not, hence, utilizable as photochromic lenses. It has further been desired to increase the Abbe's number in order to improve the chromatic aberration of the lenses of the spectacles. In general, however, the Abbe's number decreases with an increase in the refractive index. It is therefore difficult to increase the Abbe's number of the highly refractive plastic lenses for spectacles. Accordingly, it has been desired to provide a sufficiently practicable photochromic curable composition having excellent optical properties such as a high refractive index and a large Abbe's number, and excellent color density and fatigue resistance in the photochromic property.
Japanese Patent No. 2570776 (Japanese Unexamined Patent Publication (Rokai) No. 128966/1989) discloses a sulfur-containing aliphatic acrylic compound that can be cast-polymerized, that gives a cured product having a high refractive index and a large Abbe's number upon the polymerization, and that is expressed by the following formula, ##STR2##
wherein R' is hydrogen or CH.sub.3, R" is --CH.sub.2 CH.sub.2 -, and R"' is --CH.sub.2 -, --CH.sub.2 CH.sub.2 -, --CH.sub.2 CH.sub.2 CH.sub.2 -, --CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 -, --CH.sub.2 CH.sub.2 SCH.sub.2 CH.sub.2 -, or --CH.sub.2 CH.sub.2 OCH.sub.2 CH.sub.2 -.
However, it has not at all been known to use the above-mentioned sulfur-containing compound in combination with a photochromic compound to obtain a photochromic curable composition.
As a photochromic compound, on the other hand, there has been known, for example, a fulgimide compound. The fulgimide compound develops a color of a tone of orange to blue. A chromene compound and a spirooxazine compound have also been known as photochromic compounds. These compounds develop colors of tones of, generally, orange to yellow in the case of a chromene compound and reddish purple to blue in the case of a spirooxazine compound.
It is generally desired that the photochromic lens generally develops a color of a tone of grey, amber or brown. When the above-mentioned compounds are used alone, however, a desired neutral color is not obtained in many cases. An neutral color can be obtained by mixing a chromene compound, a fulgide compound or a fulgimide compound and a spirooxazine compound having different color tones at any composition ratios. For example, Japanese Unexamined Patent Publication (Kokai) No. 124790/1991 discloses a method of obtaining an neutral color by mixing a chromene compound and a fulgimide compound together, and Japanese Unexamined Patent Publication (Kokai) No. 9469/1993 discloses a method of obtaining an neutral color by mixing a chromene compound and a spirooxazine compound together. Furthermore, DE 4325154 teaches developing various neutral colors in addition to grey, amber and brown by mixing a spirooxazine compound, a chromene compound and a fulgimide compound together.